A common method for production of Methane gas trapped in a coal bed under a water aquifer is to flow it in large diameter pipes, under well pressure or by the aid of suitable pumps and blowers to collecting and storage reservoirs. However, as the gas passes through the liquid layer of the earth, an amount of water is carried by the gaseous substance, forming a mixture of gas and liquid which may interfere in the normal fluid flow of the gaseous material damaging the pumping gear and its accessories (which are often, but not necessarily, gas operated). It is thus an aim to remove such liquids and for that purpose different devices and methods have been provided.
According to one common method, a plurality of substantially liquid traps are provided in the form of discharge vertical columns fixed to the main gas flow pipe, whereby the water can be manually discharged therefrom. Said columns are distributed along the route of the main pipe and are distributed according to topographic and other considerations.
One problem with such liquid traps is the need for manual labor to reach each and every such trap and manually open it to discharge the trapped liquid which is emitted from the vertical column under pressure of the flowing gas. This operation obviously requires considerable time and man power (such manual draining may take place once a week or even every day, depending on different considerations), which at remote areas is problematic, and even more so under extreme weather conditions.
It is appreciated that in most cases there is no practical indication referring to the amount of liquid in a respective trap and that each such opening also discharges an unavoidable amount of gas, wasted to the atmosphere. The indication for the operator to close the discharge outlet of the liquid trap is the presence of gas, namely a solution of bubbles and water.
Still, in cold weather there is a serious problem in which water freezes within the liquid trap columns, and not withstanding the fact that the columns may be buried as deep as about 2 meters below ground level, freezing occurs and these may cause damage to the pipes.
It is also appreciated that the solution carries particles such as, coal-bed particles, sand and rock particles, piping debris (metal or plastic), etc.
Various patents are concerned with methods and systems for gas lift from wells and other patents are concerned with surface controlled liquid removal methods and systems for gas producing wells. The liquid concerned is typically water.
For example, U.S. Pat. No. 6,367,555 discloses a method of producing an oil, water, and gas well using a gas carrier/transport system to remove produced liquids and contained solids by altering the flow regime of the production fluids towards or into a flow regime in which gas is the continuous fluid (i.e., the rate of upflowing gas in the well is efficiently high in comparison with liquid production flow to generate plug flow, slug flow, froth flow, foam flow, annular flow, spray flow, and/or mist flow.) This is accomplished by use of supplemental gas flow (hydrocarbon or non-hydrocarbon) and/or stimulation of the production sand gas flow with a reduced pressure drop across the well once near or in a gas-continuous flow regime. This invention can be applied to any gas, oil, and/or water well with insufficient formation gas pressure to prevent liquid buildup within the well during production. The present invention utilizes a second production pipe (or the annulus between the casing and the pipe), sized to transport compressed gas from the wellhead area down into the production liquid and into the production pipe. This flow of gas will cause the well fluids to flow up the pipe by approaching or entering a gas-continuous flow regime. Once the new flow regimes have been achieved in the production pipe, supplemental gas may no longer be necessary due to increased formation gas flow without the high pressure drop which had been due to the column of liquid in the production pipe.
U.S. Pat. No. 5,501,279 discloses an apparatus and method for continually and intermittently removing water from a wellbore which penetrates a solid carbonaceous subterranean formation, such as a coalbed, while concurrently removing methane from the formation. The apparatus utilizes a linear access means which facilitates switching the apparatus from a continuous water removal mode of operation to an intermittent water removal mode of operation using wireline retrievable tools.
It is thus an object of the present invention to provide a liquid purge valve for automatic drain of liquid from a gas/liquid mixture.